The involement of PECAM-1 in cancer metastasis

目的：基质细胞，包括内皮细胞（EC），是肿瘤微环境（TME）的关键要素，释放促进肿瘤生长的因子。虽然已经研究了TME在原发性肿瘤的生长和扩散中的作用，但关于TME在调节转移性肿瘤灶的进展中可能发挥的作用知之甚少。基于大量的初步数据，我们假设在转移性肿瘤进展的晚期阶段，血管内皮PECAM-1调节TME以诱导促进转移性肿瘤生长的增殖性肿瘤细胞基因表达谱。为了验证这一点，提出了以下研究：（i）确定内皮PECAM-1参与肿瘤肺转移的分子基础（具体目标1）;（ii）鉴定PECAM-1依赖性内皮源性介质，其调节肺中转移性肿瘤的生长和进展（特定目的2）;和（iii）表征内皮PECAM-1对肺中转移性肿瘤的基因谱的影响（特定目的3）。 方法学： 具体目标1。确定内皮PECAM-1参与肿瘤肺转移的分子基础。将用野生型PECAM-1或在其介导配体结合或细胞内信号传导的能力方面突变的PECAM-1转导来自鼠肺的PECAM-1缺失内皮细胞。然后将所得细胞用于肿瘤-内皮共培养研究，以评估干扰PECAM-1功能对肿瘤细胞增殖的影响。 具体目标2。鉴定PECAM-1依赖性内皮源性介质，调节肺转移性肿瘤的生长和进展。将在来自肿瘤-内皮共培养物的条件培养基中培养的肿瘤细胞中研究体外细胞增殖，其中疑似PECAM-1调节的内皮衍生因子的表达水平已改变。这些研究中涉及PECAM-1调节的分泌蛋白的任何因子的体内意义随后将通过评估注射过表达感兴趣因子的肿瘤的小鼠中的肺转移来证实。 具体目标3。表征内皮PECAM-1对肺转移性肿瘤基因谱的影响。将使用用抗PECAM-1抗体处理的野生型小鼠和PECAM-1缺失小鼠，在肺转移的静脉内和自发模型中测定候选PECAM-1调节的生长促进基因的肿瘤细胞中的基因表达水平以及上调或下调它们的作用。临床关系：由于绝大多数癌症死亡是由转移性疾病引起的，因此更全面地了解肿瘤转移所涉及的事件对于为晚期癌症患者开发新的治疗方法至关重要。 影响/意义：微转移性肿瘤病灶晚期进展为肉眼可见的临床明显肿瘤以及TME在该过程中可能发挥的作用尚未得到有力研究。血管上表达的PECAM-1可能通过调节TME而成为转移性肿瘤晚期进展的介质。这代表了PECAM-1的一个未预料到的但可能非常重要的新功能，可能对晚期癌症的机制理解和治疗具有重要意义。

Objectives: Stromal cells, including endothelial cells (ECs), are critical elements of the tumor microenvironment (TME), releasing factors that facilitate tumor growth. Although the role of the TME in the growth and spread of primary tumors has been investigated, less is known about the role the TME might play in regulating the progression of metastatic tumor foci. Based on extensive preliminary data we hypothesize that during the late stages of metastatic tumor progression, vascular endothelial PECAM-1 modulates the TME to induce a proliferative tumor cell gene expression profile that promotes metastatic tumor growth. To test this, studies are proposed that will (i) determine the molecular basis for the involvement of endothelial PECAM-1 in tumor metastasis to the lung (Specific Aim 1); (ii) identify PECAM-1-dependent, endothelial-derived mediators that regulate metastatic tumor growth and progression in the lung (Specific Aim 2); and (iii) characterize the influence of endothelial PECAM-1 on the gene profile of metastatic tumors in the lung (Specific Aim 3). Methodology: Specific Aim 1. Determine the molecular basis for the involvement of endothelial PECAM-1 in tumor metastasis to the lung. PECAM-1-null endothelial cells from murine lung will be transduced with wild type PECAM-1 or PECAM-1 mutated in its ability to mediate ligand binding or intracellular signaling. The resulting cells will then be used in tumor-endothelial co-culture studies to assess the effects of perturbing PECAM-1 function on tumor cell proliferation. Specific Aim 2. Identify PECAM-1-dependent, endothelial-derived mediators that regulate metastatic tumor growth and progression in the lung. In vitro cell proliferation will be studied in tumor cells cultured in conditioned media derived from tumor-endothelial co-cultures, for which the levels of expression of suspected, PECAM-1-regulated, endothelial-derived factors have been altered. The in vivo significance of any factor implicated as a PECAM-1-regulated secreted protein by these studies will then be confirmed by assessing lung metastasis in mice injected with tumors over-expressing the factor of interest. Specific Aim 3. Characterize the influence of endothelial PECAM-1 on the gene profile of metastatic tumors in the lung. The gene expression levels in tumor cells of candidate, PECAM-1- regulated, growth-promoting genes, as well as the effects of up- or down-regulating them, will be determined in intravenous and spontaneous models of lung metastasis, using wild type mice treated with anti-PECAM-1 antibody and PECAM-1-null mice. Clinical Relationship: As the vast majority of cancer deaths are caused by metastatic disease, developing a more complete understanding of the events involved in tumor metastasis will be critical to developing novel treatments for patients with advanced cancer. Impact/Significance: The late progression of micro-metastatic tumor foci to macroscopic, clinically apparent tumors and the role that the TME might play in that process has not been vigorously investigated. PECAM-1 expressed on vessels may be a mediator of the late progression of metastatic tumors through a modulation of the TME. This represents an unanticipated, but potentially very important new function for PECAM-1 that may have significant implications for the mechanistic understanding and treatment of late-stage cancer.